Phase shifter



Nov. 3o, 1943. AV ALFORD 2,335,723

PHASE SHIFTER Filed, Feb. 14, 1942 FIGJ.

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55 J5 rINVENTOH. H- MMM/@F0515 vand ` In my prior Patent arrangement inwhich impedance elements may be arranged in a line in conjugaterelationship..

Patented Nov. 30, 19434 UNITED STATES PATENT QFFICVE l 2,335,723 v PHASEsnIF'rEn d n'drew Alford, New York, N. Y., assgnor to Mackay Radio andTelegraph Company, New York, N. Y., a corporationof Delaware ApplicationFebruary la, i942, Serial No. 430,899 I for., iis-maa) d Claims.

This invention relates to phase Shifters and more particularly to phaseshifting arrangements in which networks or two or more units are provided to effect the phase shift. l

In my prior Patent 2,147,807 is shown a system using two inductive orcapacitive elements arranged with respect to one another, providing aunit to produce a desired phase shift, in a twoconductor line. My priorPatent No. 2,276,910, issued March 17, 1942, shows similar phaseshift-'- ing umts consisting of two condensers in a single conductorline such as an antenna.

It is frequently desirable to obtain a' greater phase shift than canconveniently be accomplished by one of these phase shifting units. Two

such units may give suflicient phase shift but the additional weight ofso much added apparatus If two condensers are normally used for eachphase shifter, the center condenser of the combined units, formed tohave the combined-effect of theothers, will be equal in value to theseries capacity of the two outside condensers. In the case of equalcondensers this will be half the capacity of one Outside condenser.

A lbetter understanding of my invention will be had lfrom theparticularldescription thereof made with reference to the accompanyingdrawing', in which Figs. 1 and 2 are used .to explain one embodiment ofmy invention;

Fig. 2A shows a modified form of my invention;

llliig. 3 illustrates a practical radio system using a phase shifter inaccordance with my invention;

Figs. 4 and 5 illustrate embodiments of mymvention applied to twoconductor transmission lines.

2,147,807 is described an This conjugate relationship is such that thephase of wave energy transmitted along the line may be altered withoutaltering any of the other characteristics of transmission of thesewaves.

In order to secure this conjugate relationship oi network elements astaught in that patent, two elements are provided and the spacingbetweenthese elements is adjusted, and the locay tion along thelinechosen with respect to the maximum oi' standing Waves in the line toachieve the desired results. The complete mathematical derivation of theproper spacing, location, and

issued March 17, 1942, illustrates a special appli, 'cation of condenserimpedances used in single conductor lines which in this instance arepreferably antenna conductors.

It frequently occurs that a greater phase shift .than is normallyproduced by a pair .of conjugately related impedances is desired. Insuch ,cases two or more of such arrangements may be provided in the lineto achieve this result. SuchI an arrangement is shown in Fig. ,1, inwhich a single lirie L is provided with two sets of re be supported bythe wire since it requires two` additional impedances. In accordancewith my invention this additional weight'may be reduced y by moving thetwo conjugate networks together kso that the adjacent kcondensers ofeach conjugate unit are superposed. Such an arrangevment is shown inFig. 2. In this instance since Cl and C2 at the center part of thecomplete network are combined to form a single condenser unit C3, theequivalent impedanceeifect of the two units is combined in the singlecondenser C3. This results in a` condenser C3 smaller in size thancondensers CI and C2, since the impedance of this .unit must be thecombined impedance of the other two. v

Forv all single conductor lines it is preferable vto use capacitivereactances as the conjugate impedance element, since in the singleconductor line the units are arranged in series in the lines and thusthe capacitive elements when combined will be smaller than the sum ofthe two units. As is well known. the sum of series connected capacitivereactances is such that' thereciprocal of this sum is equal to the sumof the reciprocals of the other units. Accordingly, in the arrangementof Fig. 2, Y

circ-NT2 As a general rule CI and C2 are-equal, so that C3 is then equalto one-half of Cl.

The particular application of this arrangement to an antenna structureis shown in Fig. 3. In this iigure a radio translator arrangement 3,which may be either a transmitter or receiver, is shown connected to aV-type antenna comprising two sections 4, 5 and two other sections 8, 1.In order to obtain the desired phase shift between elements 4, 5, aphase sluiting network consisting of condensers Cl, C3, C2, is shown,and-a similar arrangement Cla, 03a, 02a, is shown between sections 6 andl.

It should be clearly understood that while condenser units-of this typeare generally preferred, single conductor transmission lines may useother forms of impedances. In Fig. 2A is shown a transmission line inwhich line L is provided with short sections of short circuitedtransmission lines to induce the desired impedance.- These sections areshown as SI, S2 and S3. As is well known,

if the transmission line sections are made shorter than a quarter of awavelength long, the effective impedance will be capacitive, while ifthey are made greater than a quarter of a wavelength long the effectiveimpedance will be inductive. In any case the impedance of S3 is madeequal to the sum of the impedances of SI and S2. In such transmissionline sections the known formula for deriving the impedance oftransmission lines may be applied to secure the right length for thecenter` section with respect to the outer sections. Likewise, thespacing between the units must be proper to preserve the conjugaterelationship as in the manner outlined in my previously mentioned Patent2,147,807.

It is also clear that lumped impedances such as inductive elements maybe used if desired a1- though this is generally not preferred in singleconductor transmission lines.

In Fig. 4 is illustrated a further embodiment of my invention as appliedto two-conductor transmission lines. In this gure is shown atransmission line consisting of conductors 4U, Il, across which arebridged impedance elements I3, M, 45, each consisting of a shortcircuited transmission line section. It is clear that Aif desired otherforms of transmission line section may be used, such as open-endedsections, properly adjusted in length to give the desired impedancevalue. Since these impedance elements are arranged in parallel acrossthe transmission line instead of in series in the line, the use ofinductive values rather than capacitive values is preferable. If bridgedcapacities are used, then the central element 44 would have to be equalor equivalent to twice the capacity of the other two elementsnecessitating a larger structure.-

However, when inductive elements are bridged in this manner the parallelimpedance of the centralelement will be equal to one-half the inductiveimpedance of either of the other elements 43, and 45 assuming theseelements to be equal.

IIt can,therefore, be readily seen that in the case of parallelconductor connections, as thus shown, inductive impedances arepreferable to capacitive impedances.

Instead of the use of transmission line sections, l

as shown in Fig. 4, lumped impedances such as shown at 53, 54 and 55,may be provided. It is clear that in place of the inductances 53, 54 and55 capacitive units may be provided, but in general this is notdesirable when shunt connectivzuzis- This is generally not desirablesince it is then.' necessary carefully to check both of the units itsapplied to the line to secure equal eiiects in both l sides.

while 1 have described the features of my in vention with reference tocertain specific embodiments thereof, it should be clear that .manyalter'- ations and changes may be made without departing from the spiritof my invention. For example, any of the types of units shown ormentioned herein may be used in either two-conductor or single conductortransmitting arrangements. Furthermore, the systems may be Iused inother types of antenna structures or inany arrangement of transmissionline that is desired.

What is claimed is: i

1. A phase shifting network for a conductor line comprising threeimpedance elements arranged in spaced relation connected to said line,the spacing between each twoadjacent elements being such as to produceconjugate relationship, the centrally arranged impedance having a valuesubstantially equal to the effective sum of the impedance values of theouter two impedanceunits.

2. A phase shifting network'according to claim 1, wherein said impedanceelements are condensers.

3. A phase shifting network according to claim 1, wherein said line is atwo-conductor transmission` line, said impedance elements beingconnected across said line.

4. A phase shifting network according to claim 1, wherein said line is asingle conductor line, said impedance elements being eiiectively inseries in said transmission line.

5. A phase advancing network for a single conductor line, comprisingthree condensers connected in series in said line, the spacing betweeneach two adjacent condensers being such as to produce conjugaterelationship, the centrally arranged condenser having a capacitysubstantially equal to the effective series capacity of the two outercondensers.

6. A phase advancing network according to claim 5, wherein the outercondensers of .said phase shifter have equal capacities the centralcondenser having a capacity equal to one-half of the said equalcapacity.

ANDREW ALFORD.

